Knock, concealing old, mad, eccentric plan (7)
I believe the answer is:
roadmap
'plan' is the definition.
(I have seen 'Plan of action ' mean 'roadmap' so perhaps 'plan' could also mean 'roadmap')
'knock concealing old mad eccentric' is the wordplay.
'knock' becomes 'rap' (synonyms).
'concealing' means one lot of letters goes inside another.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'eccentric' indicates anagramming the letters.
'o'+'mad'='omad'
'omad' anagrammed gives 'oadm'.
'rap' placed around 'oadm' is 'ROADMAP'.
(Other definitions for roadmap that I've seen before include "Document charting the way forward" , "Street plan" , "Plan of action" , "Plan for achieving a goal" , "Atlas for travellers" .)